This invention relates to a method for catalyzing emulsion paper release coating solutions. More particularly, it is found that dioctyl tin dineodeconate exhibits a unique combination of properties which renders it superior to conventional organo tin catalysts for paper release applications.
Diorgano tin salts having long been used to catalyze the polymerization of organosilicon compounds. They have been extensively employed, for example, in the vulcanization of silicone rubber and more recently to induce polymerization in siloxane resins used for non-stick cooking surfaces (frying pans, ovenware, etc.), as disclosed in U.S. Pat. No. 3,499,870 (Handlock et al.), which is hereby incorporated by reference.
A wide variety of organo tin compounds such as dibutyl tin dilaurate, dibutyl tin dioctoate, dioctyl tin dilaurate and dicotyl tin S,S'-bis(iso-octyl mercapto acetate) have been used in the form of aqueous emulsions to initiate curing of emulsified silicon paper release coatings. These coatings typically contain blends of silanol-terminated polydimethylsiloxanes and methylhydrogen polysiloxane in the discrete phase. The coating solutions are applied to paper from an emulsion bath and thereafter cured by heating (about 90.degree. C. to about 225.degree. C.) for a short period (&lt;60 sec.).
For paper release coating applications, a number of properties for catalyst emulsions are desirable. Long shelf stability, long bath life, good reactivity across a broad temperature range, low odor and low release are highly valued by industrial users but heretofore have not been found in combination in a single organo tin compound.
It has now been discovered that the tin salt, dioctyl tin dineodeconate, is well suited for use as a catalyst in silicon paper release coatings and exhibits all of the aforementioned properties to a degree that makes it superior to conventional catalysts. It is also easily synthesized to a high level of purity, which may account for some of its unique properties.
Accordingly, it is an object of the present invention to provide a novel method for the polymerization of silanol-containing organosilicon compositions.
It is a further object of the present invention to provide a means of securing a unique combination of properties in silicone paper release compositions including shelf stability, long bath life, reactivity over a broad temperature range, low odor and low release.
These and other objects are accomplished herein by a method of polymerizing organosilicon compounds (1) containing at least one SiOH group and any remaining silicon valences in said organosilicon compound being satisfied by radicals selected from the group consisting of silicon-bonded oxygen atoms attached to other silicon atoms to form the siloxane linkage, silicon-bonded nitrogen radicals to form the silazane linkage, silicon-bonded sulfur radicals to form the Si--S--Si linkage, Si--Si linkage, and organic groups attached to the silicon through the SiC linkage selected from the group consisting of disilylalkylene, disilylarylene, disylhydrocarbon ether linkage, monovalent hydrocarbon, monovalent halohydrocarbon, monovalent, hydrocarbon ether, nitrile-substituted monovalent hydrocarbon, ester substituted monovalent hydrocarbon, and monovalent hydrocarbon group substituted with an amino amido, and sulfide groups, there being on the average from 0.9 to 3 of said organic groups attached to the silicon which comprises contacting said organosilicon compound with (2) a catalyst comprising dioctyl tin dineodeconate, at a temperature sufficient to cause an increase in the molecular weight of said organosilicon compound.